Routing issue to Softlayer's DNS servers

I'm seeing a routing issue from Plusnet to the authoritative DNS servers SoftLayer (a hosting company) run for their customers to use (ns1.softlayer.com and ns2.softlayer.com).The servers use anycast, so packets should be routed to the closest location to the source. This should be the servers in SoftLayer's Amsterdam data centre when accessed from the UK. However, packets from Plusnet are being routed to SoftLayer's Singapore data centre instead:

This is causing quite a delay (about 350 ms) when performing DNS queries for domains hosted on these servers. Please could someone from Plusnet take a look into this? Or could someone let me know the best way of getting in touch with the Plusnet networks team?For reference, here's another traceroute from Bytemark in the UK where the route does go to Amsterdam:

Re: Routing issue to Softlayer's DNS servers

Hi there,Done a few checks on this and it seems the slowdown is at the sng01 server at the networklayer section - I tried a trace from a virgin connection which ended up around 100ms and went via slr01 and another from uk2 which went via the same server (slr01) - perhaps sng01 is just under a lot of load?Is this having an effect on your connectivity etc or is it more the increased time delay?

Re: Routing issue to Softlayer's DNS servers

Hi Matt,The sng01 routers are in SoftLayer's Singapore data center. The issue is that the route shouldn't be going to Singapore in the first place. The route should be going to the closest data centre to the source, which in this case is SoftLayer's Amsterdam data center (ams01).SoftLayer use anycast to publish/announce the same IP addresses at various different locations in the world. Other routers are then supposed to be able to choose the best route to one of the locations. It looks like Plusnet's routers are choosing the route to Singapore instead of the preferable Amsterdam route.I've run a trace on Virgin Media too. I found that this was going via po2.slr01.sr01.wdc01.networklayer.com as the penultimate hop. This is a router in SoftLayer's Washington DC data center (wdc01). Routing to Washington DC is also not the most optimal route, but is better than routing to Singapore.This routing issue causes a delay when DNS records are queried to translate a host name into an IP address. Querying a DNS record from the server in Singapore will take about 350ms longer than looking up the same record from the server in Amsterdam. This is therefore slowing down browsing to sites that use SoftLayer for their DNS.

Re: Routing issue to Softlayer's DNS servers

You could try "gateway hopping" (disconnecting and reconnecting from your router's web interface). Sometimes there is slightly different routing on different gateways. I'm on ptn-ag02 and get the same traceroute to Singapore.